IGSHPA Research Conference 2018 - Research Conference Proceedings

380 Research Conference Proceedings - IGSHPA Research Conference 2018 IGSHPA Research Track Stockholm September 18-20, 2018 Malin Malmberg (malin.malmberg@bengtdahlgren.se ) is a civil engineer at Bengt Dahlgren Geoenergi, Willlem Mazzoti is a PhD candidate at KTH Royal Institute of Technology and GSHP consultant at Bengt Dahlgren Geoenergi, José Acuña is PhD and a researcher at KTH Royal Institute of Technology and GSHP consultant at Bengt Dahlgren Geoenergi, Henrik Lindståhl is a civil engineer at Tekniska Verken i Linköping AB, and Alberto Lazzarotto is a postdoctoral fellow at KTH Royal Institute of Technology. High temperature borehole thermal energy storage – A case study Malin Malmberg Willem Mazzotti José Acuña Henrik Lindståhl Alberto Lazzarotto ABSTRACT Combining High-Temperature Borehole Thermal Energy Storages (HT-BTES) with existing Combined Heat and Power (CHP) systems running on waste fuels seems to be a promising approach to increase the energy efficiency of district heating systems through recovery of excess heat summertime from the waste-to-energy operation. This paper presents a case study from Sweden where the potential for charging and discharging waste heat at 95°C from a CHP- plant in summer into and from a HT-BTES is investigated. The interaction between the HT-BTES and the CHP-plant has been simulated with the software tool TRNSYS using the DST (Duct Ground Heat Storage Model) and a number of other TRNSYS tools. The aim of the study has been to design the size and operation of the HT-BTES with regard to energy and power coverage. Several different potential system configurations are presented in this paper, with 1 300 to 1 500 boreholes of 300 m depth. The result shows that it is possible to retrieve around 93 GWh/year of stored heat winter time, with the use of heat pumps using ammoniac as refrigerant. The discharge temperatures from the BTES range between 40-60°C, and up to 70°C in the initial discharge period. INTRODUCTION In the 1980s, Sweden was first in constructing a High Temperature Borehole Thermal Energy Storage (HT-BTES) in bedrock: the Luleå Heat Store (Nordell, 1994; Hellström, 1991). New interest for HT-BTES has arose during recent years in Sweden, especially within the district heating sector. A large part of the Swedish district heating production takes place in Combined Heat and Power (CHP) plants. These plants are often waste-to-energy plants that run at high loads and work almost continuously when they constitute a part of a waste management system, resulting in large quantities of waste heat in summer when the district heating demand is low. Furthermore, due to uneven heating demand over the year, the capacity of the CHP plants is often insufficient during peak heat demand in winter and is hence complemented by auxiliary boilers using fossil fuels or expensive biofuels as primary energy source. Operation during peak demand is costly and contributes to a larger carbon footprint. Due to the few annual operational hours the capital invested in such peak load plants is also poorly utilized. Based on this background, the possibility of shifting some of the surplus heat from summer to winter has been investigated through a case study, in order to increase the flexibility between energy supply and demand in the district heating network and to phase out fossil fuels. The investigated case involves the connection of a HT-BTES to a CHP- plant with large quantities of surplus heats in the summer (approximately 260 MWh). 2018 Research Conference DOI: 10.22488/okstate.18.000036

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